Circuit breakers are electronic switches, which are typically automatically activated to prevent damage to circuits and equipment in response to the occurrence of short circuits and/or overload conditions therein. As illustrated by FIG. 1, a conventional circuit breaker may be configured as a dual-purpose arc fault/ground fault (AFGF) interrupter 10, which can be used in a single-pole 120 VAC load application 100 that is powered by 120/240 VAC source. As shown, the interrupter 10 includes four terminals, with terminal 1 connected to the 120/240 VAC source, terminals 2 and 3 connected to a load (e.g., 120 VAC receptacle 12) and terminal 4 electrically connected (e.g., pigtail) to a loadcenter neutral.
Other conventional circuit breakers, such as mechanically operated circuit breakers (MCBs), may operate relatively slowly by using a thermal bimetal lever as a trip mechanism and this relatively slow operation may result in damage to the circuits and equipment. To address this slow speed limitation associated with conventional MCBs, electronic circuit breakers (ECBs) have been developed to achieve higher speed trip mechanisms for use with sensitive loads. For example, in a conventional ECB, a load current passes through a series element (i.e., shunt) having a very low resistance, and a voltage drop across the series element and a preset voltage may be compared in a level comparator. Then, in the presence of an excessive series voltage drop (i.e., shunt voltage), the comparator may generate an output signal to a microcontroller, which may then trigger a current controlling relay at high speed to thereby terminate an overload condition. These and other aspects of conventional ECBs are disclosed in an article by T. Deokar et al., entitled “Ultra Fast Acting Electronic Circuit Breaker for Overload Protection,” 2017 Third International Conference on Advances in Electrical, electronics, Information, Communication and Bio-Informatics (AEEICB), Chennai, India, (2017) pp. 29-32, and in article by P. Abirami et al., entitled “Electronic Circuit Breaker for Overload Protection,” 2016 International Conference on Computation of Power, Energy Information and Communication (ICCPEIC), Chennai, India, (2016) pp. 773-776.
As will be understood by those skilled in the art, the use of a low resistance shunt (e.g., 0.5 mΩ) to sense load current in an electronic overload breaker provides many advantages. For example, relative to a conventional current transducer (CT), a shunt can sense DC and very high frequency currents, does not saturate, is relatively inexpensive and typically only requires a small layout space. Nonetheless, the accuracy of the trip performance in shunt-based electronic overload breakers can be limited because variations in shunt resistance can often be significant at levels of ±10% or higher.